This invention relates to digital loop carrier transmission systems.
In a typical digital loop transmission system, such as subscriber loop carrier (SLC.RTM.) systems, digital transmission takes place between a central office and a remote terminal. Customer lines or loops are coupled to the remote terminal where analog to digital conversion takes place. One of the problems in such systems is that the length of a customer loop from the remote terminal, the cable type, and, therefore, the electrical resistance of the loop, varies widely. Thus, in cases where the loop is short, the volume of the voice signal may be uncomfortably high.
The need has been recognized to adjust the signal loss or gain in both analog and digital systems based on the resistance of the loop. (See, e.g., U.S. Pat. No. 4,056,688 issued to Stiefel and "RT Plug-In Dual Super POTS With Automatic Trunk Loss Control Channel Unit," R-TEC Systems, RPI Section 18, Issue Nov. 1, 1987.) In digital loop transmission in particular, it has been proposed to provide a loss curve which is a continuous function of the loop resistance (see R-TEC Systems, supra).